Transcript ecology and evolution

Evolution and Ecology
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The Voyage of the Beagle (1845)
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It is probable
that the islands
of the Cape de
Verde group
resemble, in all
their physical
conditions, far
more closely the
Galapagos
Islands…
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yet the aboriginal inhabitants of the two
groups are totally unlike; those of the Cape
de Verde Islands bearing the impress of
Africa, as the inhabitants of the Galapagos
Archipelago are stamped with that of
America.
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Natural Diversity
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By the Numbers –
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Estimated 2 - 100 million species, with a best estimate of
somewhere near 10 million
~1.4 million described species
~1 million described insects/ 350,000 described beetles
8,800–10,200 living bird species
~5,500 species of mammals
Great diversity exists, with each species exhibiting a
considerable degree of suitability for its natural
lifestyle
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How?
Seems unlikely
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Evolution Disclaimer
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Whether you choose to accept that evolution
is the means by which existing species
diversity developed or not, you are
responsible for learning and applying the
principles in this course.
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In short: “This course is taught from the
evolutionary paradigm.”
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What do scientists do?
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Explain
PREDICT!
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Need a theory to make predictions.
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Other major scientific theories.
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Cell theory – 1839
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Plate tectonic theory – not fully accepted until late 1960’s
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General relativity (i.e. gravitational theory) – proposed by Einstein in
1915/16.
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Gravitational waves are a requirement of the theory of
general relativity, but have never been directly detected
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Gravitational waves have been generally been accepted to exist
since 1980s.
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Chemistry – Valence bond theory and molecular orbital theory
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Competing theories in the 1930s. Now somewhat
combined – also the advent of quantum chemistry.
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What is evolution?
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Broad: The gradual process by which the
living world has been developing following
the origin of life.
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Narrow: Change in the genetic frequencies of
a population.
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What Evolution Is? By Ernst Mayr
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“Evolution is the most important concept in
biology. There is not a single Why? question
in biology that can answered adequately
without a consideration of evolution.”
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Again need theory for explanation and
prediction.
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Why is the theory of evolution important?
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Implications for people:
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Antibiotic resistance, pesticide resistance, control
of disease, human epidemiology, development of
new crops, medical treatments, conservation
biology, etc. (not to mention the ecological
implications)
Evolution provides the mechanism to address
these issues.
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Historical Background: Early contributors
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Lamark (1809): Inheritance of Acquired
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Darwin: Theory of Evolution (Origin of Species 1859)
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Characteristics (learning; meme vs. gene)
5 theories really.
Malthus: potential usually exceeds realized
reproduction for populations (including humans)
Wallace: independent conceptualization of Natural
Selection
Mendel: Genetics = currency of evolution
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Historical Background: Biological issues
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In 17th Century and prior:
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Natural history
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Medicine
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Segregated into zoology and botany
Segregated into anatomy, physiology, surgery, and
clinical medicine.
Evolution and genetics unified all these
disciplines.
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Historical Background
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Darwin’s Five Theories
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1 – The non-constancy of species
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The idea of a changing world can be considered the fact
of evolution.
2 – The descent of all organisms from common
ancestors
3 – Gradualism (no saltations, no discontinuities)
4 – Speciation by populations
5 – Natural selection
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This is the “theory” of the process of evolution.
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Historical Background
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Darwin’s Five Theories
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The non-constancy of species & common
ancestors
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Quickly accepted
Gradualism, speciation and natural selection.
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Not completely accepted until 1940’s
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Evidence for evolution
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Fossil Record
Morphology
Vestigial organs
Biogeography
Molecular evidence
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Evidence for evolution: Fossil record
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Evidence for evolution: Fossil record
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Jaw bone
evolution from
therapsid reptiles
to mammals.
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Evidence for evolution: Fossil record
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Evolution through time:
Variation through geologic periods.
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Fossils in most recent strata are often similar if not
indistinguishable from living species.
The older the strata is, the more different the
fossils.
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Evidence for evolution
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Morphology:
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This was how
species were
described as
“related” as far back
as 18th century.
Linnaean hierarchy:
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From Kingdom to
sub-species
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Evidence for evolution
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Vestigial Structures:
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Structures that are not fully functional or functional
at all.
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Evidence for evolution
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Vestigial Structures
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Blind cave dwelling animals still have eyes (that
don’t work).
Why does an ostrich have wings?
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Evidence for evolution: Biogeography
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Biogeography:
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the geographic
distribution of
organisms
those [organisms]
of the Cape de
Verde Islands
bearing the
impress of Africa,
as the inhabitants
of the Galapagos
Archipelago are
stamped with that
of America.
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Evidence for evolution: Biogeography
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Evolution through space:
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Gondwana
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Evidence for evolution
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Molecular evidence
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the more closely related two organisms are, the
more similar are their genetic structure.
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Often times, morphological traits can be
ambiguous.
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One of the most important sources of information
on phylogenetic relationships
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Mendelian genetics
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Gregor Mendel: 1822 – 1884
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What did Mendel do?
Example: Green and yellow peas
Mendelian genetics was originally
used to dispute one of Darwin’s
theories.
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Maintaining Genetic Variation – See
appendix.
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Without Selection: no loss or gain (random)
B. Hardy-Weinberg Theorem: constant allelic
frequencies are maintained if ...
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populations are large,
individuals contribute equally to genetic composition of
next generation, and
matings are random
Remember: Narrow definition of evolution = change
in the genetic frequency of a population.
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Why does this matter?
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If population is not at equilibrium –
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There are outside forces acting on the population.
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Outside forces that can change population
genetics.
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Mutations
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origin of variations, and mutation increases under stress
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Migration
Population size
Non-Random Mating
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Age, chemicals, UV-radiation
Nonrandom Mating: ∆ gene frequencies
Environmental Variance: favor some phenotypes
Effects of Selection: stable polymorphisms
Natural Selection
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Loss of Genetic Variation
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Inbreeding: rapid loss of genes
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Genetic Drift: random losses of genes
Neighborhoods: local breeding tendency
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Fixes traits quickly
Races of plants and animals
Bottlenecks: low population = reduced pool,
duration of the low population is critical (drift)
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Survivors of a near-extinction resulted in close
inbreeding 10,000 years ago.
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Current Evolution
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According to narrow definition:
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Evolution is little more than a process that
changes gene frequencies in a non-random
manner;
environmental influences direct this change
What are a few examples of recent evolution
of species that can be correlated to an
environmental stress?
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Examples
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The evolution of
pesticide resistence in
pest species
The evolution of
antibiotic resistence in
human pathogens
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note the recent
discovery of plague and
tuberculosis exhibiting
broad-spectrum
antibiotic resistence
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Insect species resistant to pesticides
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Strep resistance to penicillin
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Maintenance of variation
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So how is variation maintained in the face of
environmental pressures and natural
selection?
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Ever see a constant environment?
Microenvironmental differences exist over small
spatial scales.
Temporal heterogeneity is a common
characteristic of physical environments.
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Evolutionary Ecology
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Fusion of ecology and evolutionary theory.
Sometimes two terms used as different time scales.
An observed relationship may be explained by:
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functional, proximate or “ecological” means.
Or ultimate, evolutionary terms.
Historically, ecologists assumed many phenomena
are immutable:
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Sex ratios (always 50:50), generalist vs. specialist feeding
preferences, migration, number of offspring.
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An evolutionary perspectives recognizes these phenomena
change through time and in response to the environment.
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Evolutionary Ecology
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Evolution is a primary factor in determining
the distribution and abundance of organisms.
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A relatively new field (last 25 year).
Thus not adequately addressed in most text
books.
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“There is grandeur in this view of life, with its
several powers, having been originally
breathed by the Creator into a few forms or
into one; and that whilst this planet has gone
cycling on according to the fixed laws of
gravity, from so simple a beginning endless
forms most beautiful and most wonderful
have been, and are being evolved.”
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Charles Darwin – The Origin of Species (Last
sentence)
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